In general, the present invention relates to anti-tack agents and more specifically to surfactant treated clays useful as anti-tack agents for uncured rubber compounds.
In the manufacture of finished rubber goods, an important intermediate process step involves the application of an anti-tack agent. The anti-tack agents are used to prevent the sticking together of compounded, uncured rubber pieces which often come into contact with one another. The rubber compound may be in the form of large sheets, that are often intentionally stacked on pallets as interim storage for the next manufacturing step, or may consist as small pellets/granules of rubber. In either case, it is more desirable to prevent these rubber materials from sticking together as adhesion can result in non-processable compound that usually becomes waste product.
Anti-tack agents for rubber have been traditionally applied in one of two general fashions to the rubber stock, which include wet and dry dusting type processes respectively. The anti-tack agents of the present invention deals specifically with nonionic surfactant treated clays useful in reducing surface tack when applied to rubber stock as an aqueous clay slurry. It is well known to those skilled in the art, that mineral based slurries can be applied to rubber stock to yield a thin, detackifying coating on the surface. Such mineral based slurries have been applied to rubber stock by means of a dip tank (generally referred to in the industry as slab-dip) or by spray coating on the mineral slurry via some liquid atomization device. Minerals known to be useful in such slurry compositions include waterwashed or airfloated kaolin clays, ball clays, smectite-type clays like bentonite or montmorillonite, calcium carbonate, talc, etc. More of these minerals, with the possible exception of talc, have little if any natural affinity for the rubber stock when brought into slurry contact with the organophilic rubber surface. This is a direct consequence of the hydrophilic nature of most minerals. Thus, to enhance their chemical affinity for the rubber surface, chemical additives (primarily zinc or calcium soaps of stearic acid) have customarily been used in combination with such minerals to yield effective aqueous anti-tack compositions. It is also well known that such mineral/soap compositions will often employ other process additives (such as organic surfactants) to help aid wet-out and improve general mineral to soap compatibility. Some Literature references relative to the prior anti-tack technology are sited below:
1. G. V. Belousov, N. B. Selezneva, O. Ya. Zrazhevskaya, Yu. G. Shevchenco; "Improvement of the Formula of Release Compositions"; Kauch. Rezina, (8), 36-38 (1988).
2. S. K. Modwood, G. P. Patitsas, W. H. Waddell; "Lubricant and Use Thereof for Curing Tires"; U.S. Pat. No. 4,780,225 (1988).
To our knowledge, organic surfactants currently used in slab-dip systems have been present primarily as an auxiliary additive to augment the performance of mineral/soap anti-tack compositions. This is in stark contrast to the composition of the present invention, wherein an ethoxylated acetylenic diol, nonionic surfactant treated fine particle size kaolin clay is shown to have useful, unique anti-tack properties for various uncured rubber compounds. We know of no prior examples where an organic surface has been used strictly alone with a clay mineral to yield an effective slurry anti-tack composition. This situation, as we will later demonstrate, undoubtedly arises from the fact that most organic surfactants we have examined were not effective enough to be used alone with just kaolin clay. The ethoxylated acetylenic diol nonionic surfactants used with kaolin clay in this invention were found to offer unique wetting properties on rubber compound and therefore represent an unobvious improvement in the rubber anti-tack processing art.
Accordingly, it is an object of the present invention to provide a new, lengthy effective anti-tack composition and method which overcomes the deficiencies of the prior art as described above.
Other objects and a fuller understanding of the invention may be had by referring to the following specification taken in conjunction with the accompanying claims.
It has now been discovered that we may overcome the deficiencies of the prior art and achieve our objectives by providing a novel anti-tack composition comprised of a fine particle size kaolin clay and a nonionic surfactant of intermediate value in its hydrophile-lipophile balance (HLB) .